Have been hijacked by macsecurity-alert.com. MY husband's mac mini is using 10.9.5. When trying to log on to safari, he is stuck with a "System Alert". I have tried the force quit and can do that, but holding the shift key while trying to open Safari does not get me anywhere. I turned off the wi fi and the connection to the internet. Tried a restart and the page STILL loads with the bogus www. address and the pop up. I have even played control R with the reload page trick and cannot get any thing to work. All Safari menu options are grayed out.

Short of having a huge freakout, what should I try next?
THANK YOU!!!